Investments - Operating Lease Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Lessor, Lease, Description [Line Items]
Base cash rent	$ 116,546	$ 96,799
Variable cash rent (including reimbursables)	3,389	3,638
Straight-line rent, net of bad debt expense	1,094	2,907
Amortization of above- and below- market lease intangibles, net	334	723
Total rental income	121,363	104,067
In-place leases
Lessor, Lease, Description [Line Items]
Leases amortization expenses	$ 8,800	$ 6,700